1. Field of the Invention
The present invention relates to a pressure compensation element for compensating for pressure in an inner chamber of a housing, in particular of an electrical housing, motor housing, or gearbox, container, or the like. In particular, the invention relates to a pressure compensation element that protects the inner chamber of the housing against moisture and liquids from outside, and so forth, and furthermore offers improved protection against electrostatic discharge (ESD protection).
2. Description of the Prior Art
German Utility Model DE 295 11 683 U1 discloses a pressure compensation element in the form of a closure cap for containers, housings, bottles, or the like. The pressure compensation element is placed in the wall of the housing and has a pressure compensation diaphragm; the closure cap of at least similar shape has a cylindrical structure, since it includes a round channel in a cylinder. The opening through which the pressure compensation can take place therefore extends through the cylinder. A diaphragm is placed inside the cylinder, and the diaphragm is accommodated underneath the outer surface of the housing. If water should enter from the outside, it can accumulate on the top of the diaphragm, which over long-term use of the pressure compensation element can lead to failure of the diaphragm. Moreover, the manufacturing technique is limited to extrusion coating or injection of the diaphragm (cast-in technique), or else the diaphragm must be incorporated in a complicated way into the body of the closure cap. Although both plane and curved versions of the diaphragm are disclosed, nevertheless the curved version corresponds to the contour of only the closure cap, and thus the curved diaphragm is not equivalent to a free curvature inside the cylindrical structure. From a manufacturing standpoint, the closure cap with the pressure compensation element proves to be very complicated; a further factor is that the closure cap is not completely protected against mechanical factors from the outside of the housing by a cap. If the diaphragm is damaged, liquids can both get into the housing and escape from the housing.
From German Patent DE 196 26 792 C1, a pressure compensation element in the form of a closure element embodied as a plastic injection-molded part is disclosed. It serves the purpose of sealed, detachable closure of a complementary opening embodied in a housing, container, or the like. A filter medium, as an interface between the spaces inside and outside the housing, is integrated with the closure element; the filter medium is injected into or integrally injection molded onto the bearer part comprising at least a first thermoplastic component, and the bearer part is extrusion-coated with at least a second thermoplastic component, which in its consistency is different from the first component, to form a resultant shaped body of the closure element.
Although the technique of extrusion coating of a shaped body using an injection molding material offers effective reception of the diaphragm, nevertheless, the technique of plastic extrusion coating requires at least one indentation inside which the diaphragm is placed, and the indentation forms the opening through which the pressure compensation can take place. This embodiment also has the disadvantage that a cavity, in the form of an indentation above the diaphragm, develops that can fill with liquid and put the diaphragm out of operation. Moreover, there is no possibility of introducing the diaphragm into the receptacle in a cued form. Moreover, there is no possibility of protecting the diaphragm, by means of a cap, closure, or the like, against mechanical influences from the direction of the outer side.
Moreover, pressure compensation elements are also known which have diaphragms that are welded or clamped onto a bearer structure. The welding can be done by means of a laser-beam welding process or an ultrasonic welding process. In that process, the diaphragm is mounted on the outside of the receiving structure, but this structure is neither protected against moisture, liquids, and the like, from the outside nor offers protection against mechanical influences. Damage to the diaphragm from liquid or a mechanical influence therefore often causes the failure of the pressure compensation element.